The present invention relates to swim fins.
With swim fins conventionally used to obtain the thrust required for swimming, the level of the propulsive force to be obtained largely depends on their particular configurations. Various configurations of swim fins have already been proposed and, for example, Japanese Patent Publication No. 1976-35999 discloses a swim fin having a propulsion blade which comprises a curved main portion, auxiliary blade portions and opposite side rails so that a large water-contact area may allow a large amount of water to be caught by the propulsion blade and a powerful propulsive force may be obtained by thrusting such amount of water rearward. In addition, Japanese Patent Application Disclosure Gazette No. 1990-7672 discloses a swim fin having a propulsion blade which is made of relatively hard material and provided along opposite side edges of the blade with slits, respectively, wherein these slits are filled with relatively soft material so that a middle portion of the blade defined between the slits may be easily bent in the vertical direction around its root portion and both up- and downkick of a swimmer may produce a desired propulsive force.
For many swim fin designers including those of the above-mentioned well known swim fins, obviously it has been one of the most essential interests to catch an amount of water as large as possible and thereby to thrust this amount of water rearward as powerfully as possible.